In the production of integrated circuits, it is known to image a number of masks with different configurations onto a substrate whose surface is modified by exposure to light. The substrate is subjected to physical and chemical changes between successive images, such as a removal of the exposed or unexposed part of a photoresist applied to the substrate and the etching of underlying layers. The photoresist is conventionally termed "positive" in the first and "negative" in the second instance.
Whereas vertical structuring is readily possible today in the processing of integrated circuits by modern doping techniques and highly developed methods for the deposition of layers onto semiconductor surfaces, the possibilities for horizontal structuring are considerably more limited. A refinement of the lateral structuring of integrated circuits of the semiconductor disk is therefore the object of considerable present efforts.
While in the past it used to be the practice to contact the pattern-bearing mask directly with the substrate during the exposure step, the greater present-day requirements for accuracy have more recently led to imaging the mask onto the substrate with interposition of an objective (projection exposure). Moreover, there is also a tendency to simplify the production of several identical patterns on a single wafer by a stepwise shifting of the image instead of using a mask provided with a corresponding plurality of patterns.